PRODUCT CONTAINING β-ALUMINA AND PROCESS OF PREPARING THE SAME.



UNITED STATES PATENT OFFICE.

LEWIS E. samns 038 TO NOB-ION comm, IASSLCHUSET'IB.

PRODUCT CONTAINING fl-ALUIINL m 1,263,708. Io Drawing.

To all whom it may concern:

Be it known that we, Lewis E. Sawmill! and Bar HILL Warm, citizens of the United States, residing at Niagara Falls, in the of Niagara and State of New York, have invented certain new and useful Im- Containing fi-Aluprovements in Products recesse of Preparing the saine,

prepared up to the present time exclusively in the electric furnace, and adapted for abrasive, refractory and other uses, said products consisting 0 or containing material roportions of alumina in a crystalline modi cation which is designated as -a1umina (beta-alumina). This term is to distinguish the modification from the crystal form of alumina occurring in nature (corundum, sa phire, ruby, etc.) and which is also forms when most aluminous materials, including bauxite, are melted in the electric furnace, this heretofore known crystal form of alumina being new for convenience designated a-alumina (alpha-alumina.)

B-alumina in relatively very small proportions has been recently observed associa with a greatly prepon crating proportion of a-alumina in certain electric urnaee products which were prepared by meltin substantially pure alumina (alumina an ntially free from fluxing impurities) and permitting the melt to so idify into a pig, in the manner disclosed in a prior U. S. patent granted A ril 12 1910, to George N. Jeppson and wis l5 Saunders, o. 954, 'rl-alumina has also been observed in small ro ortions in association with a compoun .Al,0, with which a-alumina has entered into solid solution (see 01 'Amzri' can Chemical Society, March 1916, page e have now observed that B-alumina, or a crystalline product containing large proortions of dalumina, occurs at times in the orm of platy crystal in in interior portions of the pig or ingot of substantially ure alumina prepared in accordance wit the patent above mentioned. Such giated masses or bodies rich in (l-alumina are istinguished from the main y of tl e pig by exhibiting a highly characteristic plat structure. In the commercial manu- AHD MY KILL WHITE, OF KIAGABL FALLS,

OI WOBGEB'L'BB.

indication of Letters Patent. Application M arch l, 1917.

NEW YORK, ASSIGN- IASSAOHUBETTB, L CORPORATION OF 0! PREPARING THE SAME.

Patented Apr. 23, 1918.

sci-in Io. mam.

facture of abrasives from such materials it has heretofore been the unvarying practice to crush and grade the entire pig or ingot, (after cleaning off any unconverte crust) without reference to the small roportion of laty material therein, this p aty material a few per cent.

constituting at the most grobably not exceeding five per cent.) of

a commercial abrasive grains.

B-alumina is readily distinguished under the microscope from the alpha variety, being characterized b a lower refractive index and a higher doub e refraction. The value for the c-ray is approximately 1.629 to 1.65, as compared with 1.76 for a-alumina. The value or the o-ray is ap roximately 1.665 to 1.680, as compared wit 1.768 for ci'alumina. fl-alumina has also a lower specific nvity, 3.30 as against 3.90 for a-alumina.

0th forms are exagonal, both uniaxial, and both have a negative optical character. The grain of (talumina, while hard, is relatively weak. Tests of certain specimens have indicated that the hardness of B-alumina, while suflicient for commercial abrasive urposes is distinctl less than that of the a pha modification. 'fhe combination 0 a relatively weak structure and hard sulliciently great to act as a good abrasive but somewhat less than that of the hardest known abrasive, indicates for fi-alumina certain s ial applications in the abrasive field; or example, in finishing and polishing operations where individual grains if very hard and tough cause scratches.

Our researches have now shown that it is possible to p epare in the electric furnace, by fusing a suitably compounded charge, a product, as a pig or ingot, containing ractically any desired proportion of fi-alumina; and even to prepare such plroducts consisting substantially or practice ly exclusively of B-alumina. We will proceed to descr be the best means now known to us for accomplishing this result, it being understood that our invention is not limited to the use of the particular salts or compounds hereinafter specifically mentioned as convertsay, which are capa- 1 nts, that is to ble w en added to the chargepf aluminous at its partial or Our invention likewise includes broadly a product of fusion of an aluminous material, which product contains material proportions of crystalline alumina of the beta variety. By material proportions we mean such proportions, usually in excess of ten per cent, as will affect to a-material or practical extent the abrasive or other propertiespf the product.

The best means known to us for converting alumina, for example a charge of amorphous oxid of aluminum, A1,0 free from notable proportions of the oxids of silicon and titanium, into crystalline alumina of the beta modification, consists in adding tothe charge, and preferably intimately commingling therewith, a relatively small proportion of a salt of an alkali metal, such as sodium or potassium. Very minute additions, say under one per cent. of sodium carbonate, for example, show some effect the beta modification being distinguishable in the product b a microscopic examination. It will be un erstood of course that a microscopic examination does not lend itself to an exact quantitative determination of the proportion of B-alumina present; but it is reasonable to assume that the small pro ortions of B-alumina heretofore observe in products obtained by the electric furnace fusion of precipitated alumina may be attributable to the presence in such alumina of small accidental traces of sodium carbonate, or of other alkali compounds, such compounds being as is well known exceedingly diflicult of removal from the precipitate. However this may be, we have found that by introducing sodium carbonate in varying amounts into a charge of otherwise substantially pure alumina we are able to reduce a pig or ingot containing B-alumma, the proportion of B-alumina in the product tending to rise ra idly as the proportion of added sodium car onate is increased. The alkali metal is in part at least retained in the roduct (proba ly in the form of aluminatei and is calculated in the analysis as Na The followin tabular statement shows certain observe relations between the amount of N a,0 in the product and the roportion (approximate of the product w ichexists in the beta m 'fication.

Hop to product. U. 32% 5 b0 10% In the last-mentioned example the dense portions of the pig were found to contain about eighty per cent. of B-alumina; the porous or cellular portions about seventy per cent.;' and the segregated platy portions about eighty to eighty-five per cent.

In "ompmmding the charge somewhat more of the alkali compound is added than appears in the product, inasmuch as some loss by volatilization or otherwise is to be expected, the amount of this loss depending upon time and temperature of fusion, the proportion of alkali originally present, and per aps other factors. For example, the above mentioned product containing 2.57% of Na,0 resulted from the fusion of a charge which was compounded to contain Amorphous alumina, Al,,O,, 96.0 per cent. Na,O 3.7 per cent.

together with about 0.8% of iron oxid and silica.

So far as observed, the formation of B-alumina is dependent upon the basic component of the converting agent (Na or Na,(O), the CO being so far as known without efiect. Therefore sodium aluminate ma be regarded as equivalent to sodium car onate, as may also other sodium salts or compounds, including caustic soda, sodium sulfate, etc. All sodium compounds are not, however, equally eilicient as converting agents, that is to sav, for inducing formation of the beta modification. For example, the use of sodium chlorid is attended with heavy volatilization, whereby the major portion of the sodium compound is eliminated, and relatively small proportions of dalumina are formed in the product. Potassium salts and com ounds are in general essentially similar in t eir action to the corresponding sodium salts. Lithium compounds efiect the conversion, but apparently to a lesser degree than the corresponding sodium or potassium salts.

We believe it to be characteristic of all of these alkali additions that the yield under the operating conditions a product or a substance, the precise nature of which is as yet undetermined, which exists at least in part, at the moment of solidification of the molten mass, in the vapor phase. This is indicated in various ways, but especially it is ocularly shown by the fact that the ingot or pig, or portions thereof, have a more or less porous or cellular structure, showing either cells or channels, or both. It is probable that the substance, whatever it may be, which is present in the vapor phase, is a material of ve high boilin -point, since otherwise it won d be expect to disappear before or during the fusion stage. For conyenience we may ammo that the material is sodlum alummate or some dissociation product thereof, ssibly sodium metal or sodwnroxid, or t e corresponding products containing potassium, etc. cnever in this specification and claims reference is made to compounds of sodium, it is to be understood not their chemical equivalents in this art are thereby included.

The ctfcct of sodium compounds in bringing about a transformation of the alumina to the beta modification may be wholly or in part neutralized by certain oxide having an acid character, as SiO, and TiO,. this case material proportions of B-alumina are formed only in case the soda is present in sutlicient roportions to overcome the inhibiting ten ency of the acid oxide.

The product containing a material roportion of, or consistin essentially o alumina is crushed, gra ed and bonded in the customary way, a ceramic or other bond, such as vulcanite. being used as may be preferred.

\Ve claim 1. As a new product, a pig or mass containing a material roportion of fl-alumina.

2. As a new p net, a pig or mass containing in excess of fifty per cent. of B-alumine.

3. As a new roduct, a pig or mass consisting essentia ly of fi-alumina.

4. s a new product, a pig or mass having as its principal components aand B- alumina, the latter in material proportions.

5. As a new product, a pig or mass having as its principal components aand B- alumina, the latter is predominating proportions.

6. As a new product, an aluminous abrasive whereof the ins containa material proportion of [3-11 umina.

7. As a new product, an aluminous abrasive whereof the grains contain a pmdomimating proportion of B-alumina.

8. s a new product, an aluminous substance containing a material pro rtion of B-alumina associated with a inm compound.

9. As a new product, an aluminous substance containing a predominating roportion of fl-alumina associated wi a sodium compound.

10. As a new product, an aluminous substance consisting essentially of B-alumina associated with a sodium compound.

11. The rocess of preparing fi-alumina, which consists in fusing an aluminous material with a converting agent, the latter in suflicient quantit to eflect the transformation of a materia proportion of the alumina in the charge into the beta modification.

12. The mecca of preparing fl-alumina, which consists in fusing an aluminous material with a sodium com ound, the latter in sufiicient quantit to e ect the transformation of a matcria proportion of the alumina in the charge into the beta modification.

13. The recess of preparing p-alumina, which conslsts in fusing an aluminous material with sodium carbonate, the latter in suflicient quantity to effect the transformation of a material proportion of the alumina in the charge into the beta modification.

14. The process of preparing fl-alumina, which conslsts in fusing an aluminous material with a converting agent, the latter in suflicient quantity to efi'ect the transformation of more than half of the alumina in the charge into the beta modification.

15. The recess of preparing B-alumina, which consists in fusing an aluminous material with a sodium com ound, the latter in sutlicient quantity to c act the transformation of more than half of the alumina m the charge into the beta modification.

16. The rocess of preparmgfi-alumma, which consists in fusing an aluminous material with sodium carbonate, the latter in suflicient quantity to efl'ect the transformation of more than half of the alumina in the charge into the beta modification.

In testimony whereof we afiix our signatures.

LE WIS E. .SAU NDERS. RAY HILL W HITE. 

